The soybean cyst nematode (SCN) Heterodera glycines Ichinohe is considered the most economically debilitating disease-causing pathogen to affect soybean cultivation (Noel, G. R. (1992) in Riggs, R. D., Wrather, J. A. (eds) Biology and management of the soybean cyst nematode, APS Press, St. Paul, Minn., pp 8–10), causing losses of up to one billion dollars annually (Kim, D. G. et al. (1997) J. Nematol. 29:173–179). Several Hg types of SCN (Nieblack, T. L. et al. (2002) J. Nematol. 34:279–288) exist in the field (Riggs, R. D. et al. (1988) J. Nematol. 23:149–154) and several soybean genes that confer resistance have been identified. The most important of these genes have been mapped to linkage groups G and A2 of the soybean genetic map (Webb, D. M. et al (1995) Theor. Appl. Genet. 85:136–138; Concibido, V. C. et al. (1996) Theor. Appl. Genet. 93:234–241; and Meksem, K. et al. (2001) Theor. Appl. Genet. 103:710–718).
Several approaches have been undertaken to characterize nematode-responsive gene expression patterns within feeding sites of the soybean root. Changes in mRNA abundance were studied by in vitro translation to proteins (Hammond-Kossack, K. E. et al. (1989) Physiol. Mol. Plant Pathol. 37:339–354; Potenza, C. L. et al. (1996) J. Nematol. 28:475–484; and Oberschmidt, I. et al. (1996) Fourth annual meeting of the European union AIR-CAP on Mechanisms for resistance against plant parasitic nematodes, Toledo, Spain, p. 13). Subtractive hybridization of cDNA libraries prepared from nematode-infected and uninfected roots has yielded “infection-specific” clones. This approach has been utilized in tomato plants infected with root-knot nematodes (Van der Eycken, W. et al. (1996) Plant J. 9:45–54), and in potatoes infected with cyst nematodes (Niebel, A. et al. (1995) MPMI 8:371–378). Likewise, several PCR-based libraries have been constructed to permit the cloning of “giant cell-specific” transcripts (Wilson, M. A. et al. (1994) Phytopathol. 84:299–303; and Bird, D. M. et al. (1994) MPMI 7:419–424). Use of the differential display technique has yielded several interesting candidate genes in the Arabidopsis-Meloidogyne interaction (Vercauteren, I. et al. (2001) MPMI 14:288–299) and the soybean-SCN interaction (Hermsmeier, D. et al. (1998) MPMI 11:1258–1263). Promoter-GUS fusion (Opperman, C. H. et al. (1994) Science 263:221–223) and promoter trap (Barthels, N. et al. (1997) The Plant Cell 9:2119–2134; and Puzio, P. S. et al. (1998) Physiol. Mol. Plant Pathol. 53:177–193) approaches have also been implemented to identify nematode-responsive loci.
In a previous report (Vaghchhipawala, Z. E. et al. (2001) MPMI 14:42–54), we showed that several genes were up-regulated within the syncytium during colonization of the root by SCN. We determined the map locations of some of the soybean genes responsive to nematode infection by locating them on the public soybean map (Shoemaker, R. C. et al. (1996) in D. P. S. Verma and R. C. Shoemaker (eds) Biotechnology in Agriculture, No. 14, Soybean: genetics, Molecular Biology and Biotechnology, CAB International, Wallingford, Oxon, UK, pp. 37–56). A particularly interesting candidate was phosphoribosylformylglycinamidine ribonucleotide (FGAM) synthase. This gene mapped to the same 3.0-cM interval of Linkage Group G where the major soybean SCN resistance locus Rhg1 maps (Mudge, J. et al. (1997) Crop Sci. 37:1611–1615).
FGAM synthase was of interest because of its coincident location within the genomic interval containing Rhg1 and its up-regulated expression within the nematode feeding site. The enzyme FGAM synthase catalyzes the fifth step of the de novo purine biosynthetic pathway, effecting the ATP-dependent transfer of the glutamine amido group to the C-4 carbonyl of FGAR (5′-phosphoribosyl-N-formylglycinamide). To investigate this soybean gene further, we isolated and characterized two FGAM synthase loci. The two loci were highly similar in sequence. Analysis of the two copies revealed distinct functions and/or expression profiles during development and syncytium formation. As is described herein, the promoters of both FGAM synthase copies were found to contain novel nematode responsive domains that are active during syncytium formation.